Known in the art is a system for water recovery from water-containing waste, particularly from urine, comprising a urine intake and storage unit, a urine and flush water pretreatment unit, a unit for water reclamation from urine [Lawrence D. Noble, Jr., Franz H. Schubert, and Robert P. Werner, "An Update of the Readiness of Vapor Compression Distillation for Spacecraft Wastewater Processing", 22-nd International Conference on Environmental Systems, Seattle, 13-14 July, 1992, No. 921114].
The unit for water reclamation from urine comprises: a distillation assembly, a liquid pump assembly, a vacuum pump, fluids control and pressure control assemblies, a recycle filter tank assembly, built-in control instruments.
The distillation assembly is designed as a rotary lobe compressor with a temperature sensor, a centrifuge consisting of an evaporator and a condenser separated by a thin wall, a liquid level sensor and a centrifuge speed sensor. The distillation assembly includes an electric motor coupled directly to the compressor by a magnetic coupling and to the centrifuge through a reduction gear. The electric motor has an integral cooling jacket and an electric motor speed sensor.
The fluids pump assembly is a four-tube peristaltic pump, one tube of which is used to pump urine to the distiller, two tubes are utilized to pump the concentrate from the distiller, and the last tube is used to pump the distillate (condensate). The interior of the pump housing is under vacuum.
The vacuum pump is intended for the removal of noncondensable gases and vapor from the distillation assembly and is designed as a four-tube peristaltic pump provided with a cooling jacket that causes the noncondensable gases and vapor to be cooled down.
In the known system, pretreated urine is supplied from the urine intake and storage unit to the circulation loop of the unit for water reclamation from urine, where the urine circulates through a filtering tank which is simultaneously a concentrate tank, until a required degree of water recovery from urine is reached, the circulating urine being delivered to one of the sides of the rotating heat-transfer surface of the centrifuge, where the urine is heated and water is evaporated therefrom in an amount corresponding to the heat input. The urine distillation process is carried out under vacuum. Water vapors are pumped out, pressurized by the compressor thereby increasing their pressure, and delivered to the other side of said rotating heat-transfer surface, where the water vapors are condensed and the condensation heat heats the urine obtained at the opposite side of said surface. The resulting condensate is pumped through a condensate quality monitoring sensor and supplied for subsequent use.
The disadvantages of the known system are as follows: a high power consumption of the vapor compressor, governed by the distiller throughput capacity; a reduction in the distiller throughput capacity with an increase in the concentration of the solution being evaporated, this leading to a longer time of the system operation and to its greater power consumption; the presence of special peristaltic pumps for pumping urine at the distiller inlet and outlet, which increases the mass and power consumption of the system and decreases the reliability of its operation.
Also known in the art is a multistage distiller for preparing fresh water from sea water, comprising a rotatably mounted vertical hollow rotor, an electric motor, heat-transfer plates made from a metal with a high thermal conductivity and annular partitions arranged alternately in the rotor, annular heat insulation gaskets separating them. The plates, partitions and gaskets constitute distillation stages with evaporation and condensation surfaces and concentrate- and condensate-collecting chambers arranged at the periphery, separated by annular partitions. The distiller is also provided with a preheating heat-exchanger with separate channels for sea water, condensate and concentrate circulation, arranged over the edges of the distillation stages, the channels for sea water circulation being connected at the inlet in parallel with vertical sea water distribution collectors (risers), and at the outlet--with the evaporation surfaces of the distillation stages, whereas the concentrate and condensate channels are connected in parallel at the inlet to the concentrate- and condensate-collecting chambers, respectively, and at the outlet--to the concentrate--and condensate-tanks coupled to means for discharging said fluids.
In the distillation stages (except the first and the last ones) the evaporation surface is the upper side of the preceding stage plate, and the condensation surface is the lower side of the subsequent stage plate; the first distillation stage has no evaporation surface and is provided with an inlet branch pipe for heating vapor, the last stage is connected to a vacuum line for the removal of noncondensable gases and provided with a coil which serves as the condensation surface. The inlet of the coil is connected to the sea water feeding means, and the outlet of the coil is connected to sea-water tanks. [Richard L. Clark and LeRoy A. Bromley, "Saline water conversion by multiple-effect rotating evaporator", Chemical Engineering Progress, vol. 57, No. 1, pp. 64-70].
Vapor is fed to the lower plate, providing heat supply for evaporation. A low pressure (vacuum) is set up at the upper (the coldest) plate to provide the necessary temperature gradient. The liquid to be processed, supplied to the distiller (in the present case, sea water), after heating owing to condensation of vapor from the upper plate at the coil, comes to the preheating heat-exchanger, in which each of the flows is heated to a temperature close to the evaporation temperatures on the plates, and then parallel flows of the liquid being processed is directed to the center of the plates.
Up to 50% of the feed liquid is evaporated as it gradually flows along the plates in the form of a thin film, whereby an intensive heat transfer is ensured. Vapor is condensed on the bottom (lower) surface of the higher-located plates. The condensate and concentrate flow toward the external edge of the plates under the effect of centrifugal forces to the concentrate- and condensate-collecting chambers, respectively, while the partitions separating the chambers preclude mixing of the concentrate and condensate. These latter flow down to the preheating heat-exchanger, providing heating of the feed liquid to be processed. Further, the concentrate and condensate are removed from the distiller.
The presence of the heat-exchanger for preheating the liquid to be processed makes the distiller design more complicated and increases the mass of the distiller.
The known distiller is also disadvantageous in that in the case of its shutdown under zero gravity conditions the liquid being processed will be carried over to the condensate, and this may lead to deterioration of the quality of the processed water.
As the degree of the liquid evaporation is increased to meet space requirements, the total temperature gradient will rise due to an increase of temperature depression; this will add to the power consumption and a decline in the overall efficiency of the distiller.
Furthermore, from RU, A, 2046080, there is known a system for water recocvery from urine aboard spacecraft, comprising a urine intake and pretreatment unit, a unit for water reclamation from urine, a reclaimed water sorption/catalytic purification unit, all said units being connected in series. The urine intake and pretreatment unit comprises a means for storage and delivery of pretreatment chemicals and flush water, a gas-liquid separator for separating transport air from urine, a pretreatment chemicals feed indicator, an intermediate tank of separated urine, which is designed as three elastic containers separated from each other, each of said containers being provided with an empty/full sensor and solenoid valves, and a urine feed line. The unit for water reclamation from urine comprises a urine evaporation apparatus provided with a urine circulation loop with a urine heating means, a brine tank connected through a solenoid control valve to the urine circulation loop, a condenser (cooling heat-exchanger), a condensate purge line provided with a condensate intermediate tank with a condensate discharge pump, a line for the removal of humid noncondensable gases, comprising a separator. The reclaimed water sorption/catalytic purification unit is constituted by two columns, one of the columns containing a catalyst and a sorbent arranged in beds and the other containing granular polymeric salt carriers; said unit also comprises a water collection and storage tank, water quality monitoring sensors and solenoid valves.
The urine evaporation unit of the known recovery system is designed as an evaporator provided with an evaporation partition consisting of capillary-porous polymeric semi-permeable membranes, this partition dividing the evaporator into a urine zone through which the liquid flow is passed and an air zone, the air circulating in an independent closed air loop. Evaporation of the urine occurs at atmospheric pressure, whereas making-up with fresh pretreated urine with flush water occurs due to a vacuum generated in the urine loop as the urine is gradually evaporated.
The urine circulation loop comprises a urine circulation pump, a urine electric heater, an air-separating and storing filter, a solenoid valve.
The air circulation loop comprises a condenser, a separator with porous elements, an air blower, and a moisture trap.
The disadvantages of the known system for water recovery from urine are as follows: a low intensity of the evaporation and condensation processes at atmospheric pressure and, consequently, a need in large evaporation and condensation surfaces, this leading to an increase in the mass of equipment; a decrease of the evaporation rate and a deterioration of the condensate quality because of gradual clogging of the capillary-porous membranes and loss of their selective permeability, and, consequently, a reduction in the service life of the evaporator and of the column of the condensate sorption/catalytic purification unit, this leading to an increase of the spare units; absence of the condensation heat recuperation, leading to high power consumption.
Likewise known in the art is a rotary vacuum distiller for water recovery from aqueous solutions, particularly from saline water {U.S. Pat. No. 3,200,050], which comprises a casing, an electric motor, a hollow rotor rotatably mounted in the casing, heat-transfer plates secured to the rotor, forming a zone of evaporation of the liquid being processed and a zone of condensation, a separating unit which separates the evaporation and condensation zones, devices for distributing the liquid being processed, a circulation loop for the liquid being processed with a means for heating said liquid, a line for feeding the liquid to be processed and a line for discharging condensate, noncondensable gases and concentrate.
The zone of evaporation of the liquid being processed is shaped by the exterior surfaces of inclined heat-transfer plates, and the zone of condensation is formed by the interior surfaces of said plates and by the walls of the rotor.
The separating unit which separates the evaporation and condensation zones is designed as a cylinder with a louver and a compressor installed below said cylinder.
The throughput capacity of the distiller is sufficiently high, but it is not intended for providing a high coefficient of water recovery, and therefore it is not suitable for operating in space, where a high degree of water recovery is required.
Moreover, feeding the liquid to be processed and evaporated to the evaporation surfaces, discharging the concentrate and condensate from the distiller, are feasible only in the presence of gravitation and with a vertical arrangement of the apparatus.
The overall dimensions, mass and power consumption of the distiller do not meet the requirements set for space hardware.